1. Field
The following description relates to a power factor correction circuit. The following description also relates to a power factor correction circuit and a related method for simplifying a circuit and improving a power factor and Total Harmonic Distortion (THD) by changing a reference signal in real time to fit to an input signal in consideration of only the frequency and phase information of the input signal, when the input signal that is inputted to a converter changes. The following description also relates to a corresponding converter.
2. Description of Related Art
A converter receives input power and supplies required power to a load. The type of the voltage supplied to the input power is AC power and the type of the current supplied to the load is DC power. The current flowing through the load is similar to the current of the input power, so a phase difference is generated between the voltage and the current of the input power and a reactive power loss is generated accordingly. The reactive power loss decreases a power factor. Here, the power factor is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit.
Because of this issue, it is useful to reduce the phase difference between the voltage and the current of input power in order to improve a power factor. By improving the power factor, less power is lost due to the use of the converter. Also, because the current of input power is influenced by the current flowing through a load, when the current supplied to the load has a frequency and a phase that are similar to those of the voltage of the input power, the phase difference between the current and the voltage of the input power is potentially reduced. For example, one of the factors that reduce an efficiency of power transmission from a power plant is an increase in reactive power due to a phase difference that occurs between voltage and current. Accordingly, the power factor is improved when the phase difference between the voltage and the current of power is sufficiently reduced. That is, the smaller the phase difference between voltage and current, the larger the Power Factor Correction (PFC) is, and accordingly, the larger the phase difference, the smaller the PFC.
Additionally, the current of input power has to have a sine wave as its form in order to improve THD. That is, switching of a power switch of a converter may interfere with other devices. As a result, it is advisable that the harmonic components of the current of input power are small in order to minimize the interference, as discussed above. Furthermore, an index that numerically shows the amount of harmonic components is the THD and it is required to be close to a sine wave having a single frequency in order to reduce THD during operation.
Accordingly, it is useful for the current supplied to a load to have a sine wave characteristic, with a frequency and a phase that are similar to those of the voltage of input power, in order to improve a power factor and THD.
Many alternative correction circuits for improving a power factor and THD have been proposed. For example, in one alternative correction circuit, an approach is used in which it is attempted to improve a power factor and THD by generating an internal signal by using information matched with the phase and frequency information of an input signal.
However, in this alternative correction circuit, a reference signal is produced by calculating the period of an input signal and then generating a clock signal corresponding to the calculated period. Accordingly, it is difficult to generate a reference signal having accurate phase information according to issues that arise when calculating the period of the input signal.
Further, in the alternative correction circuit, the alternative correction circuit uses a process of converting input voltage into current at a predetermined level and then converting the current back into voltage. Accordingly, the alternative correction circuit also encounters the issue that it is complicated to generate a reference signal and there is a requirement for a precise sensing circuit to be able to successfully perform the converting.
In the alternative correction circuit, a reference signal is generated on the basis of only the information for one approximated period, in which the reference signal is generated to fit to the previous frequency and then applied to the next period. Accordingly, in this approach, the reference signal is based on the information of the previous period, and thus when the frequency of the present period changes, an error is generated due to the discrepancy that results from the difference between the reference signal as generated and the reference signal that would correspond to the changes that occur. Accordingly, distortion is generated in the signal, corresponding to the error.
Further, in the alternative correction circuit, a clock signal is used, as described above, to generate a reference signal. However, a clock generator for generating a clock signal calculates one period of an input signal, as discussed above, and generates a programmed sine wave corresponding to the period, accordingly. Therefore, when an input signal is not a sine wave, distortion is necessarily generated between the input signal and a reference signal generated on the basis of a clock signal, due to the imperfect modeling of the input signal using the generated sine wave.